{extend name='mycss/base'/}
{block name="style"}
<style>
    div.container {
        width: 30em;
        border: 1em solid green;
    }
    div.box {
        box-sizing: border-box;
        -moz-box-sizing: border-box; /* Firefox */
        -webkit-box-sizing: border-box; /* Safari */
        width: 50%;
        border: 1em solid red;
        float: left;
    }
</style>
{/block}
{block name="main"}

<div class="container">
    <div class="box">这个 div 占据左半部分。</div>
    <div class="box">这个 div 占据右半部分。</div>
</div>

{/block}